This invention relates to the field of building control systems, and more particularly, to ventilation and life safety dampers for use in building control systems.
Building control systems control various aspects of a building and include features directed to comfort, safety, lighting and other aspects. With respect to comfort, one aspect of a building control system includes heating, ventilation and air conditioning (HVAC). An HVAC system involves conditioning of the air within an area, zone or room (collectively, a “room”). Such conditioning includes providing heated air, cooled air, fresh air, circulated air and/or the like to the particular room depending on various factors. The HVAC system includes a system of ducts that terminate in particular rooms. The termination points are controlled by ventilation dampers or damper systems. Each ventilation damper/damper system is operative to open and close to control the flow of air through the respective termination point and into a room. Accordingly, ventilation dampers/damper systems (collectively, “dampers”) are used for temperature control, pressure regulation, air circulation and/or replacement of stale air within the rooms of a building.
Basic two-position dampers are positionable into either a fully opened or a fully closed position. This two-position system provides for either full air flow or no air flow into a room. Modulated dampers are also available. Modulated dampers are positionable in many intermediate positions between open and closed. These intermediate positions can be advantageous when attempting to maintain the temperature in a room at a constant desired comfort level.
Many HVAC systems use only two-position dampers and do not incorporate modulated dampers. Other HVAC systems are designed with a combination of two-position dampers and modulated dampers. In these combination systems, the modulated damper is used for comfort control such as regulating the temperature in the associated room. In both systems, the two-position damper may be used as a safety feature in the event of fire and smoke. In particular, in certain situations it may be advantageous to vent heat and smoke away from a room. In other situations, it may be advantageous to seal a room to avoid fanning existing flames. Fire safety codes typically do not allow for modulated operation in the presence of smoke or fire in order to ensure basic operation of the damper. Thus, even if buildings include modulated dampers, they must also include two position fire and smoke safety dampers.
The two-position fire and smoke control damper generally employs a two-state actuator operable to open or close the damper. The two-position damper actuator generally includes power supply circuitry, motor control circuitry, an electric motor, and an actuator/damper interface. The power supply circuitry receives AC or DC input, transforms the input, if appropriate, and delivers power to the motor control circuitry. The motor control circuitry generally passes the appropriate power on to the electric motor, causing an interface adaptor from the actuator to deliver an appropriate torque to the actuator/damper interface. The actuator/damper interface is simply a gear arrangement or other mechanism or component used to join the output shaft of the actuator to the damper operator mechanism which is operable to open or close louvers of the damper. Accordingly, the actuator is positioned on or near the damper to allow the actuator/damper interface to connect to the damper operator mechanism.
One challenge in the manufacture of damper actuators is meeting certain UL and local code requirements. An example of such a requirement is that an actuator must open or close damper louvers, shifting the louvers from 0 to 90°, within a certain time period, such as fifteen seconds. However, when the actuator motor experiences a heavy load, the motor may not rotate as fast as expected, and it may take longer than expected to open or close the damper louvers. For example, if an actuator is controlling a damper upstream of a large fan, the required torque load increases due to air flow on the damper blades. In this situation, more power must be provided to the electric motor in order to rotate the electric motor at the speed required to open the damper louvers within the allotted time. Accordingly, it would be desirable to provide an actuator having the ability to increase the power to the actuator motor when the actuator motor is experiencing a heavy load.
In the above-described situation, it is advantageous to increase power to the actuator motor. However, in other situations, it would be advantageous to decrease power to the actuator motor. For example, when an actuator motor is driven too fast, unnecessary wear may result on the gear train of the actuator. Furthermore, when an actuator is driven all the way to its physical stop position at a high speed, the gears of the actuator slam to a stop as the actuator motor drives the gears with excessive force against the physical stop. Accordingly, it would be advantageous to decrease the power to the actuator motor when the gear train is moving at an excessive speed or when the gear train approaches the physical stop point. As a result of reduced speed in certain situations, less wear on the gears would result.